The invention discloses an online monitoring device for anchor sections of overhead lines. The device comprises a first host 1, a first slave 2, a second host 3 and a second slave 4. According to thedevice, through a micro-electro-mechanical acceleration sensor, a distance measuring sensor, a temperature and humidity sensor, a satellite data receiving module, a wireless communication module, a wireless networking module and a radar module, the height change of a balance weight string of an overhead line compensator is monitored in real time, the overhead line acceleration value change, hard point change, oscillation amplitude change, disconnection and compensator lag fault information and ambient temperature and humidity, position and time information are monitored in real time, and the data is preprocessed and then sent to a cloud data analysis and processing center, so that a support is provided for an overhead line maintenance mechanism. According to the device, the problems that the states of the overhead lines cannot be acquired in a full time period in vehicle detection and artificial patrol modes and the feedback speed is low are solved, so that the maintenance work is moretargeted and the efficiency is higher, and thus the quality of a tractive power supply system is improved, and the train operation safety is improved.